skip to Main Content
+49 7071 565 44 850 Facebook

Locus Information: A Locus (ASIP gene)

Inheritance: autosomal recessive

→ Horses with two or one copies of the functional Agouti variant (AA, Aa) will be bay in color. Only horses with two non-functional copies of the Agouti variant (aa) will be black.

General Information:

  • The Agouti (ASIP) gene (A) is involved with the production of both red (pheomelanin) and black (eumelanin) pigments. It regulates the relative amounts of each pigment produced in melanocytes (pigment-producing cells) in different regions of the horse’s body.
  • A functional version (AA or Aa) results in a horse that has a base color of bay with black points (mane, tail, legs, ear tips). Red and black pigments are both produced and deposited into hairs on the body, and only black pigment is is produced in the points.
  • Two non-functional copies (aa) result in a horse with a black base color, because dark pigment is produced over the entire body.

Possible Genotypes:

Genotype: Effect:
AA Two functional copies → the horse is bay, black pigments are restricted to legs, head, mane and tail.
Aa One functional and one non-functional copy → the horse is bay but carries the factor for black.
aa Two non-functional copies → the horse is black. No red pigment is produced, only black pigment.

A horse’s base color is determined by the combination of its Agouti and Extension genes. A horse will have the genetic potential for bay or black, as determined its combination of Agouti variants: AA, Aa, aa. However, the combination of variants at the Extension locus (chestnut) can stop the black pigment from being produced, so that the horse will be chestnut (ee). We may then say it is “carrying black”, if it has one or two copies of the Agouti recessive variant (Aa, aa).

  AA Aa aa

Carries factors for black





Carries factors for




Carries factors for

chestnut and black



Carries factors for



ee AAee



Carries factors for black


Carries factors for black


Test information: This test detects an 11 basepair deletion in the ASIP gene.

Rieder, S., Taourit, S., Mariat, D., Langlois, B., Guerin, G.: Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus) Mammalian Genome 12:450-455, 2001. Doi: 10.1007/s003350020017.

More information may be found on the website: Online Mendelian Inheritance in Animals.

Shades of bay: All of these horses will be either AA or Aa. The genetic variants responsible for the different shades and color intensities are not yet known.

Test #: H200

Sample: Blood, Hair

Price: 35 € (net)

Time: 10-14 days

Back To Top